Niobium-tantalum separation



NIOBIUlVI-TANTALUM SEPARATION Harley A. Wilhelm, Ames, Iowa, and RaymondA. Foos, Kenmore, N. Y., assignors to the United States of America asrepresented by the Atomic Energy Commission No Drawing. ApplicationAugust 15, 1955 Serial No. 528,569

Claims. (CI. 23-23) This invention deals with the separation of niobiumand/or titanium values from tantalum values contained in an aqueoussolution by solvent extraction.

Niobium and tantalum occur together in a great many ores, for instance,in the columbite-tantalite-type ores. These ores contain the niobium andtantalum in the form of their pentoxides mainly in association withferrous oxide and manganous oxide. The formula of columbitetantalite orecorresponds to [(Nb, Ta)O (Fe, Mn); it also contains small quantities oftin oxide, titanium oxide, aluminum oxide, and silica. Fergusonite isanother ore containing both, niobium and tantalum; it has the formulaY(Nb, Ta)O The residue obtained in processing blomstrandine alsocontains both niobium and tantalum values.

Tantalum has a great many uses in metallurgy and in particular as acomponent of alloys. It is mostly desirable to incorporate the tantalumin pure form, and for this reason it was necessary to devise a processby which the tantalum could be effectively separated from the niobiumassociated therewith. Niobium, being in the same group of the PeriodicTable of Elements as tantalum, has very similar chemical properties, andfor this reason the separation of the two elements has been found ratherdiflicult.

One process has been developed which uses an aqueous hydrofluoric acidsolution of the tantalum-niobium ore. In the preferred embodiment ofthat process free hydrofluoric acid is best present in a concentrationof about 0.4 N, and this solution is extracted by contact with asubstantially water-immiscible organic ester, alcohol, ketone oraldehyde containing at least 5 carbon atoms whereby the tantalum istaken up by an organic extract phase while the niobium remains in theaqueous solution. The process is described in copending applicationSerial No. 387,338, filed by Harley A. Wilhelm and James V. Ken-igan onOctober 20, 1953, and granted on October 16, 1956, as Patent No.2,767,047. The process of this copending application has given verysatisfactory results. However, it has the disadvantage that the freehydrofluoric acid in the aqueous solution causes quite some corrosionproblems since glass as well as most metals react therewith.

It is an object of this invention to provide a process for theseparation of tantalum and niobium values by selective solventextraction from hydrofluoric acidcontaining aqueous solutions by whichthe above described disadvantage is overcome.

More specifically it is an object of this invention to provide a processfor the separation of tantalum and niobium values by selective solventextraction from hydrofluoric acid-containing aqueous solutions whichdoes not require the handling of highly corrosive solutions.

It has been found that by adding an amine to the aqueous hydrofluoricacid-containing solution prior to extraction, the corrosiveness ispractically eliminated and satisfactory selective extraction is obtainedfrom such an 2,8?Lh2 Patented Jan. 2?, 1959 amine-containing solution.The quantity of the amine should be great enough to bring the pH to avalue of at least 4 so that the corrosiveness of the solution is reducedto a minimum. On the other hand the extraction is better if the pH valueis not higher than 6, as will be demonstrated later. tween 4 and 6 isconsidered optimal.

While aliphatic as well as aromatic amines are suitable for the processof this invention, aromatic amines are preferred because they yield ahigher degree of separation. Alkanol amines were found to be among thebest-operative amines; also aniline and aniline derivatives (hereinafterreferred to generically as aniline), and here again the l-alkanol-substituted anilines, proved excellent. Mixtures of varioussolvents, for instance, of aniline with monoethanolamine gave also goodresults.

The amines per se do not function as selective extractants. A few ofthem at best accomplish a fair total extraction but no separation tospeak of. For the purpose of selective extraction a solvent is thenadded to, or contacted with, the amine-containing aqueous solution.

A great many solvents were tested; a suitable selective solvent, it wasfound, had to have at least 4 carbon atoms in the molecule, and it hadto be substantially waterimmiscible; esters, aldehydes and ketones werefound operative, the ketones yielding the 'very best results. Solventsthat were successfully used are cyclohexanone, isophorone, mesityloxide, methyl isobutyl ketone, methyl n-hexyl carbinol, tributylphosphate, ethylacetoacetate, and water-immiscible amines other thanthose having a hydroxy group. For instance, branched primary amines thathave a tertiary alkyl structure and a total carbon content of between 12and 24 atoms per molecule were found satisfactory; m-toluidine provedalso operative. The amines in some cases were preferably used in dilutedform, and fuel oil, kerosene, turpentine, toluene, and heptane werefound to be suitable diluents.

A great many tests were carried out using various cornbinations of amineand solvents. For these tests a columbite-tantalite ore was processed65% by weight of which consisted of tantalum and niobium pentoxides andwhich also contained some iron, titanium, manganese, aluminum, silicon,and tin. For each test 10 grams of the finely ground ore were mixed with8.0 grams of sodium hydroxide and 4.0 grams of sodium peroxide, and thismixture was then heated at 650 C. for 30 minutes. The mass was cooledand then leached with about 300 ml. of hot 1.0 M aqueous sodiumhydroxide solution whereby the aluminum, tin, manganese, and siliconwere dissolved. The insoluble residue was then separated and leachedwith about 200 ml. of a hot solution of 5.0 M nitric acid to which atrace of hydrogen peroxide had been added. By this treatment the ironand titanium were dissolved; thesolution was removed by filtration. Theresidue which was practically pure niobium and tantalum pentoxides wasthen dissolved in about 5 ml. of concentrated hydrofluoric acid.

The hydrofluoric acid solution thus obtained, the stock solution,contained the pentoxides in a weight ratio of 52Ta O :48Nb O The totalcontent in pentoxides amounted to 517 g./l. which corresponds to amolarity of about 1.45. The total acidity of the stock solution was 17.3M while the F concentration was 15.3 N. For the extraction testssummarized in the table below aqueous initial solution, which had beenobtained by diluting 22 ml. of the stock solution to ml., was usedexcept where indicated otherwise. One volume, usually 10 ml. of theinitial solution, was contacted ineach case, after the addition of theamine, with two volumes of the organic solvent or solvent mixture. Thevalues given in the table as Ta/Nb separation factors represent the Forthese reasons the pH range bequotient of distribution ooeflicient ofTazdistribution coeflicient of Nb whereby the distribution coefl'icientis concentration in the organic phasezconcentration in the aqueousrafiinate. The total extraction indicates the peraevneea phenyldiethanolamine was used as the amine and diethyl ketone as the solvent(experiment 24).

Some experiments were carried out (not shown in the table) in whichequal volumes of solvent and initial socentage of the Ta O -l-Nb O thatwas extracted into 5 lution were contacted instead of two volumes ofsolvent the organic phase based on the content of the initial per onevolume of initial solution. It was found that solution. by the use of asmaller relative quantity of solvent a The aqueous and the organicphases obtained by the lower total extraction and a lower separationfactor were extraction were analyzed. For this purpose ammoniumobtained. 1 hydroxide was added to the solutions (after addition ofAnother example will now be given in which a acetone to facilitatefiltration) whereby tantalum and stage extraction run was carried out;'10 ml. of a feed niobium were precipitated as the hydroxides; thesewere solution, 5 ml. of scrub solution, and ml. of solvent then removedby filtration and calcined at 800 C. for at were contacted in eachcycle. The solvent was introduced least 2 hours. X-ray fluorescenceanalysis was applied at the first stage, the feedat the .ninth stage andthe to mixtures which contained not .less than 2% of either 15 scrubsolution at the fifteenth stage; a countercurrent ingredient, whilespectographic analysis was used for flow was obained by this. The"solvent was dlethyl kcmixtures that contained less than 2% of eitherniobium tone, the feed solution a hydrofluoric acid solution conortantalum. taining 260 g. of tantalum pentoxide plus mobium pent- TotalTa/Nb Expt No. Amine pH Solvent Extraction, Separation Percent Factordiethanolamine.... 5 diethyl ketonc 1.0 not determined.

do 5 12.5% BPA +87.5% di- 90.0 21.9.

ethyl ketone. ....(10 7 diethyl ketone 0.33 not determined. -do 7BPA-+50% diethyl 82.3 1.28.

ketone. --.-do 7 5% BPA2+95% diethyl 18.0 1.41.

ketonc. io 9 0.72 not determined monoethanolamine 5 55. 0 5.62.triethanolamine.- 5 59.2 6.68. diethylethanolamine 5 57.8 7.07.aminoethylethanolamine- 5 53. 4 2.82. 3-aminopropanol 5 ,do 53.0 11.8.....do 5 12.5% BPAZ+87.5% di- 91.7 18.3

. ethyl ketone. aniline 5 5% tBPA diethyl 60.8 321.

6 One. 50%b.vol.ofaniline+50% 5 do 55.6 200.

monoethanolamine. phenylethylethanolamine. 5 63. 9 268. .do 5 dlethylketone 38.8 506. 5 34.0 128. 5 cyclohexanone 59. 0 19.3. 5 isophorone.46. 8 65.8. 5 mesityl oxide... 40. 2 76.5. o 5 tributyl phosphato 49.161.0. m-tolyldiethanolarniue-- 4 diethyl ketone. 40. 6 358. phenyldiethanolamine... 4 cyclohexanone. 47. 4 103. do 4 diethyl ketone" 35. 0657. 4. ethyl aeetoacetate- 41. 7 105. 4 isophoroue 43. 2 219. v '4inesityl oxide; 38. 9 286. 4 methyl isobutyl ketone 30. 8 281. 4diethylketone 36.4 152. 4 isophorone. 52. 5 97.8. 4 mesityl oxide... 43.7 97.2. 4 tributyl phosphate 48. 8 70.8.

1 indicates that; undiluted stock solution was used for theseexperiments.

1 EPA indicates a mixture of primary aliphatic amines with highly branmary amino-nitrogen is directly attached to a tertiary carbon atom: themixture principally contained amines ched alkyl chains, in which theprifrom CrQHgsNHz to Oral-13 N11 had a molecular weight of -227, a spec96 0., a boiling range (at 760 mm.) for 590% at 223 to 240 0., a neutralequ 1,423 at 25 0., color 1 of the Varnish Scale and was insoluble inwater.

The results of the experiments show that under idenamines. Theexperiments also demonstrate that the pH values of 7 and 9 are too highand give very low separation factors and in some cases even low totalextraction. It is furthermore obvious that the diluted initial solutionyielded better separation factors than theextractions carried out fromundiluted stock solution. (Compare for instance experiments 16 and 17;experiments .27 and 31; experiments 24 and 29.) The total extractionvalues did not vary radically with diflerent'solvents but the separationfactors diflered drastically. With aromatic amines the solvent yieldingthe best separation factors was diethyl ketone (experiments 16, 22 and24). The very highest separation factor of 657 was obtained when ificgravity of 0.812, a flash point of ivalent of 191, a refractive index ofoxide (52:48) per liter, phenyl diethanolamine, and having a pH value of5; the scrub solution was prepared from an about 0.5 M hydrofluoric acidby adding phenyl diethanolamine thereto until the pH value wasapproximately 4. The organic phase obtained after the 15 "stagescontained about 52% of the total oxides, and

these 52% were practically pure tantalum pentoxide; its niobium contentwas p. p. m. This shows that practically 100% of the tantalum oxide hadbeen extracted. The aqueous rafiinate contained practically all of theniobium pentoxide and less than 300 p. p. m. of tantalum.

The process is also effective for the separation of titanium values fromtantalum values since titanium like niobium stays in the aqueoussolution.

Instead of using hydrofluoric acid, columbite-tantalite or similar oreshave'also been dissolved in an aqueous soluasvnoea tion of potassiumhydroxide. Also in this instance the ore was first leached with sodiumhydroxide and nitric acid as described above; the residue was thentreated with a potassium hydroxide solution, e. g. of a concentration of2 M. A solution was obtained thereby in one instance which hat. a pHvalue of above 14 and which contained 65 g. of pent oxides per liter(1.63 M). This type of solution was contacted with various solvents,such as ketones, alcohols, amines, ethers, esters, hydrocarbons andorganic phosphates in an attempt to extract the niobium and/or tantalum;but no extraction took place. However, when.

this solution obtained with the potassium hydroxide was neutralized withcitric acid to a pH value below 7 prior toextraction, some extractionoccurred. For instance, ml. of the above basic solution were neutralizedwith 7g. of citric acid to a pH of 4.0 and then extracted with an equalvolume of a mixture containing 75% by volume of methyl ethyl ketone andby volume of a mixture of branched primary amines which had a similartertiary alkyl structure as that used for some experiments sum marizedin the table but principally from 18 to 24 carbon atoms per molecule, amolecular weight between 269 and 353, a neutral equivalent of 343, aboiling range of 262-315 C. for 5 to 70%, a specific gravity of 0.845, arefractive index at 25 C. of 1.460, color 15 of the Varnish Scale and aflash point of 127 C. A total of 9.4% of the pentoxides was extracted;44% of these oxides was tantalum oxide. In the remaining aqueoussolution 55% of the total oxides were tantalum oxide. Thetantalum-niobium separation factor was 1.58.

It will be understood that the process of this invention is applicableto ores other than those mentioned in the introduction and to variouskinds of solutions which contain niobium and tantalum values.

What is claimed is:

1. A process of substantially reducing the corrosive eflect ofhydrofluoric acid on metal and glass equipment used in the selectiveextraction of tantalum values from an aqueous hydrofluoric acid solutioncontaining said tantalum values together with niobium values bycontacting said solution with an organic substantially waterimmisciblesolvent selected from the group consisting of cyclohexanone, isophorone,mesityl oxide, methyl isobutyl ketone, methyl n-hexyl carbinol, diethylketone, tributyl phosphate, ethyl acetoacetate, m-toluidine and amixture of diethyl ketone plus primary alkyl amines having branchedalkyl chains in which the primary aminonitrogen is directly attached toa tertiary carbon atom and in which the amines contain from 12 to 24carbon atoms per molecule, said process comprising the step of adding tosaid hydrofluoric acid solution, prior to contacting with the solvent,an amine selected from the group consisting of phenylethylethanolamine,m tolyldiethanolamine, phenyl diethanolamine and aniline in a quantityto adjust the pH value of said hydrofluoric acid solution to between 4and 6.

2. The process of claim 1 wherein the solvent is diethyl ketone.

3. The process of claim 2 wherein the amine is mtolyldiethanolarnine.

4. The process of claim 2 wherein the amine is phenyl diethanolamine.

5. The process of claim 2 wherein the amine is phenylethylethanolamine.

References Cited in the file of this patent UNITED STATES PATENTS1,719,650 Chamberlain July 2, 1929 2,562,571 Partridge July 31, 19512,767,047 Wilhelm et a1. Oct. 16, 1956 OTHER REFERENCES Ellenburg etal.: Analytical Chemistry, vol. 26, No. 6, June 1954, pp. 1045-1047.

Nathan, in Chemical Abstracts, vol. 47, col. 6849(i), 1953.

Stevenson et al.: Analytical Chemistry, vol. 25, No. 10, October 1953,pp. 1517-1519.

Hopkins: Chemistry of the Rarer Elements, D. C. Heath and Co., N. Y.,1923, pp. 225-226.

Milner et al.: A. E. R. E. Report, C/R 895, pages

1. A PROCESS OF SUBSTANTIALLY REDUCING THE CORROSIVE EFFECT OFHYDROFLUORIC ACID ON METAL AND GLASS EQUIPMENT USED IN THE SELECTIVEEXTRACTION OF TANTALUM VALUES FROM AN AQUEOUS HYDROFLUORIC ACID SOLUTIONCONTAINING SAID TANTALUM VALUES TOGETHER WITH NIOBIUM VALUES BYCONTACTING SAID SOLUTION WITH AN ORGANIC SUBSTANTIALLY WATERUMMISIBLESOLVENT SELECTED FROM THE GROUP CONSISTING OF CYCLOHEXANONE, ISOPHORONE,MESITYL OXIDE, METHYL ISOBUTLY KETONE, METHYL N-BEXYL CARBINOL, DIETHYLKETONE, TRIBUTYL PHOSPHATE, ETHYL ACETOACETATE, M-TOLUIDINE AND AMIXTURE OF DIETHYL KETONE PLUS PRIMARY ALKYL AMINES HAVING BRANCHESALKYL CHAINS IN WHICH THE PRIMARY AMOINO NITROGEN IS DIRECTLY ATTACHEDTO A TERIARY CARBON ATOM AND IN WHICH THE AMINES CONTAIN FROM 12 TO 24CARBON ATOMS PER MOLECULE, SAID PROCESS COMPRISING THE STEP OF ADDING TOSAID HYDROFLUORIC ACID SOLUTION, PRIOR TO CONTACTING WITH THE SOLVENT,AN AMINES SELECTED FROM THE GROUP CONSISTING OFPHENYLETHYLETHANOLAMINE,M-TOLYLDIETHANOLAMINE, PHENYL DIETHANOLAMINE ANDANILINE IN A QUANTITY TO ADJUST THE PH VALUE OF SAID HYDROFLUORIC ACIDSOLUTION TO BETWEEN 4 AND 6.